With the preponderance of capacitive touchscreen sensor interfaces, the industry demands high signal-to-noise ratios (SNR) to impart reliable performance and to overcome the presence of various types of noise in the environments in which touchscreens typically operate. Such noise includes, for example, noise generated by LCDs, power supplies and environmental noise. These requirements generally impose a need for touchscreen controllers to be supplied with clean ripple-free power, which is typically delivered to an analog core in the touchscreen controller, as well as to touchscreen drive lines operably connected to the touchscreen controller. As a result, on-chip low drop-out regulators (LDOs) are often used to provide clean, ripple free power supplies for touchscreen controllers.
Since capacitive touchscreen controllers are used in many hand-held consumer applications, very low power consumption is required of them. If a clean ripple-free power supply is employed in a touchscreen controller, LDOs in the controller may be configured to shut down to provide additional power savings. Power down signals EN can be delivered to a touchscreen controller by an external pin, but doing so requires additional hardware.
What is needed is a touchscreen controller that consumes little power but that does not require additional pins or hardware.